Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.52   13.629%   $271.0279   $271.03   $271.05   $271.00  
  Purchase #2 $165.94   10.220%   $182.8991   $182.90   $182.90   $182.90  
  Purchase #3 $193.55   12.300%   $217.3567   $217.36   $217.35   $217.40  
  Purchase #4 $189.28   4.485%   $197.7692   $197.77   $197.75   $197.80  
  Purchase #5 $166.73   11.103%   $185.242   $185.24   $185.25   $185.20  
  Purchase #6 $175.78   10.487%   $194.214   $194.21   $194.20   $194.20  
  Purchase #7 $222.97   12.255%   $250.295   $250.30   $250.30   $250.30  
  7 purchase totals = $1,352.77       $1,498.8039   $1,498.81   $1,498.80   $1,498.80